Typical directional control valves utilize a binary-type fluid power positioning system in which the directional control valve is directed to one of two or three positions. In many existing two-position valves, the directional control valve is coupled to an actuator assembly with a double-acting piston. When the directional control valves is in the first position, air (or other fluid) is directed to one side of the piston, while air on the second (opposite) side of the piston is vented to atmosphere. When the directional control valve is in the second position, air is directed to the second side of the piston, and air on the first side of the piston is vented to atmosphere.
In some embodiments of a directional control valve, the valve includes a third position of the spool within the valve body, which is physically located between the first and second positions of the spool relative to the valve body. The third position is characterized by a different type of fluid connectivity relative to the first and second positions. For example, in the third position, all inlet and actuator ports might be isolated (i.e., none of the four ports are in fluid communication with each other), or both actuator ports might be connected to an exhaust port.
A directional control valve is typically implemented by a first body (typically called the spool) that slides linearly within a second body (typically called the valve body). The valve body includes a series of external ports, which are either isolated from fluid communication, or exposed to fluid communication with adjacent ports by the geometry of the spool. FIG. 1 shows a schematic of a conventional two-position valve spool and body geometry. In the figure, the inlet port is represented by S (supply), and the exhaust ports represented by E (exhaust), while the first and second actuator ports are represented by A and B, respectively. Note that, as shown in the figure, the exhaust port is typically separated into two geometrically distinct ports, which facilitates the reciprocal fluid connectivity between exhaust and actuator ports that characterizes a directional control valve. That is, since the spool can only expose fluid communication between adjacent internal ports, and since the two positions provide reciprocal connectivity between the exhaust and actuator ports, each actuator port must be adjacent to each exhaust port. Further, since the connectivity in the first and second valve positions is reciprocal, the ports must also be arranged in an anti-symmetric manner, such that sliding the spool from the first to the second position will reciprocally connect the respective supply, exhaust and actuator ports. That is, if the supply and exhaust ports are positioned to the right and left, respectively, of the first actuator port, then the supply and exhaust ports must be positioned to the left and right, respectively, of the second actuator port. Thus, one can deduce that the geometric conditions required to provide the reciprocal connectivity of a directional control valve are adjacency (i.e., a supply and exhaust port must be adjacent to each actuator port) and anti-symmetry (i.e., the geometric configuration of supply and exhaust ports relative to the first actuator port must be mirrored with respect to the second actuator port). As a result of these geometric conditions, the standard architecture of a directional control valve is embodied by a 5-port architecture, as shown in FIG. 1. This architecture can be referred to as a 5-port geometry, since the valve body contains five internal and external ports, where the exhaust port is associated with two physical ports (i.e., the five physical ports in the valve body are associated with four distinct fluid pressures). As shown in the figure, when the valve spool is in the first position (P1), the inlet port (S) is in fluid communication with the first actuator port (A), and the exhaust port (E) is in fluid communication with the second actuator port (B). When the valve spool slides to the second position (P2), the inlet port (S) is in fluid communication with the second actuator port (B), and the exhaust port (E) is in fluid communication with the first actuator port (A). These are the two fundamental positions of a directional control valve.
As previously mentioned, a third position can be introduced between the first and second positions of the valve spool. The three standard configurations of port connectivity for the third position are shown schematically in FIGS. 2 through 4. Specifically, FIG. 2 shows a third position configuration in which all ports are isolated; FIG. 3 shows a third position configuration in which the inlet port is connected to both actuator ports (and the exhaust port is isolated); and FIG. 4 shows a third position configuration in which the exhaust port is connected to both actuator ports (and the inlet port is isolated). Note that implementation of these three variations require essentially no substantially changes in the directional control valve architecture relative to the basic two-position architecture. Specifically, as shown in FIG. 2, the first variation (all ports isolated) requires no changes in valve spool or body geometry, relative to the two-position spool and body. As shown in FIG. 3, the connectivity in which the inlet port is connected to both actuator ports requires only minor variations to the spool geometry, and in particular, requires that the center lobe on the valve spool be narrower than the nominal spool geometry. Finally, as shown in FIG. 4, the connectivity in which the exhaust port is connected to both actuator ports requires that the two outer lobes of the valve spool be narrower than the nominal spool geometry. Thus, the third-position functionality embodied in prior art is enabled by minor variations on the nominal valve geometry (and specifically requires either no changes or slight changes in the spool geometry).
In some applications, it may be desirable for the third-position behavior that provides fluid communication between the two actuator ports and simultaneous fluid isolation of the inlet and exhaust ports. This application describes some valve spool and body configurations that provide this third-position behavior.